The invention relates to a switching pad or plate having electroinsulating flat bodies arranged essentially in parallel to one another, to which at least one current-conducting contact path is assigned which has disconnecting switches disposed in series which are actuated by pressure on one of the flat bodies, with contact pins being assigned to the disconnecting switches and, subjected to spring force, resting against the contact path.
Switching pads are known, for example, from German Patent Document DE 38 21 305 A1 in which two switching strips are installed in a switching pad made of a rubber-elastic material, each switching strip comprising a plurality of contact plates which adjoin one another by their end edges and are held together by expander cords which extend through them. A contact path extends in these contact plates, and the arrangement is such that each of the contact plates has contact points at its ends which are connected with the contact points of the adjacent plate-shaped element. When the switching pad is touched and when, as a result, the plate-shaped elements are moved apart, the contact points are disconnected so that the electric circuit is interrupted.
As a rule, switching pads of this type cannot also be constructed to be sufficiently sensitive for causing a switching operation when pressures are low.
A switching pad of the type is known from British Patent Document GB 1 394 064 in which leaf springs are provided either on one side or one both sides of an insulating base plate. The leaf springs from the current-conducting contact path. At certain points, the leaf springs are provided with bores through. Contact pins made of steel reach through the bores via a wide head which is in each case pressed from the outside against the leaf springs which in turn, are pressed against the head as a result of their intrinsic elasticity. When pressure is exercised on the leaf springs, the head of the contact pin is therefore released so that the current path is interrupted. This applies to the embodiment shown in the above-mentioned British Patent Document GB 1 394 064 having a contact pin which is fixedly arranged on the base plate. This also applied to a variant which is also shown in which the contact pin, by means of two contact heads each provided on its end, is held between two leaf springs arranged on both sides of the base plate. In constructions of this type, the triggering of a switching operation may be endangered if the pressure on the device is carried out directly in the area of the switching head of a contact pin. This is because, even when leaf springs are actuated, the contact pin may still rest there with a certain area of its circumference against the bore in the leaf springs. A secure switching operation is therefore possible only when corresponding monitoring devices are used for monitoring the current flow. A sensitive operation is not possible using constructions of this type.
It is therefore an object of the invention to develop a switching pad or plate of the initially mentioned type in such a manner that, a sensitive operation is possible and that also, the whole area of the switching pad or plate can be divided into small areas. Touching of these areas results in an interruption of the contact.
These and other objects are achieved by the present invention which provides a switching pad comprising electroinsulating flat bodies arranged substantially in parallel to one another, at least one current-conducting contact path assigned to the flat bodies, the current-conducting path having disconnecting switches disposed in series and which are actuated by pressure on one of the flat bodies. Contact pins are assigned to the disconnecting switches and each has a contact head and an end facing away from the contact head, the contact pins biased by a spring force to rest by the contact heads against the contact path. The contact pins are firmly connected by the end facing away from the contact head with one of the flat bodies. At least one of the flat bodies forms an insulating guide in which the contact pins are movably held.
With the present invention the whole area of the switching pad or plate can be provided with contact elements whose spacing is determined only by the size of the contact heads and the insulating distance required between adjacently extending branches of the contact path. This invention therefore permits a very fine subdivision of the switching pad or plate area with contact elements. Because of the small size of the contact elements and the direct connection of the switching pins with one of the flat bodies, the invention also permits a sensitive operation.
In certain embodiments of the invention, characteristics are provided which permit a compact and flat construction.
According to certain embodiments of the invention, two switching circuits are formed which act independently of one another. A switching pad or plate which is constructed in this manner has two redundant security systems and can therefore be used particularly where increased demands are made on security. In this case, the invention may expediently be implemented such that the contact path assigned to one of the plates or pads and the contact heads interacting with it extend at a distance from the contact path assigned to the other plate or pad. In this case, the contact path of one of the plates or pads expediently extends in each case in the center between the parallel branches of the meandering contact path of the other plate or pad.
In certain embodiments of the invention, sensors are assigned to the indentations which, when the switching pin is actuated, are actuated by the contact head interrupting the contact path. The reason is that this makes it possible to determine in each case at which point the interruption of the contact path has taken place. This is an important advantage, for example, for security devices by means of which it is also to be determined where an operator is situated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.